1. Field of the Invention
The present invention generally relates to a self-expanding stent delivery system for delivering a self-expanding stent.
2. Background Information
Delivery systems for deploying endovascular stent grafts, self-expanding stents or balloon expandable stents are well-known in the field of medical technology. One example of a stent delivery system for delivering a self-expanding stent is disclosed in International Patent Publication No. WO 98/23241, which corresponds to U.S. Pat. No. 5,968,052.
As has been explained in the before-mentioned citation a self-expanding stent is a stent which expands from a compressed delivery position to its original diameter when released from the delivery device, exerting radial force on the constricted portion of the body lumen to re-establish patency. One common self-expanding stent is manufactured of nitinol, a nickel-titanium shape memory alloy, which can be formed and annealed, deformed at a low temperature, and recalled to its original shape with heating, such as when deployed at body temperature in the body.
One important factor in delivering the stent is a controlled precise retraction of the retractable outer sheath. What is needed is a delivery system which provides for a controlled and precise retraction of the retractable outer sheath and enabled the physician to accurately determine proper positioning of the stent, as well as track the retraction of the outer sheath.
Known delivery systems suffer, however, from the draw-back that the retraction forces are often too high, especially in cases where the stents are covered with layers made from body-compatible materials or the like so that the friction forces between the stent and the outer sheath may become excessively high.
In view of the above, it will be apparent to those skilled in the art from this disclosure that there exists a need for an improved self-expanding stent delivery system for delivering a self-expanding stent. This invention addresses this need in the art as well as other needs, which will become apparent to those skilled in the art from this disclosure.